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BS EN 17710:2024 Plant biostimulants. Detection of Listeria monocytogenes, 2024
- undefined
- 1 Scope
- 2 Normative references
- 3 Terms and definitions
- 4 Principle [Go to Page]
- 4.1 General
- 4.2 Pre-enrichment in selective liquid medium
- 4.3 Enrichment in/on selective media
- 4.4 Plating out on selective solid media
- 4.5 Confirmation
- 5 Culture media, reagents, antisera
- 6 Equipment and consumables
- 7 Sampling
- 8 Preparation of test sample [Go to Page]
- 8.1 General
- 8.2 Liquid (water-based) formulations
- 8.3 Liquid (oil-based) emulsifiable concentrate (EC) formulations [Go to Page]
- 8.3.1 General
- 8.3.2 Solid wettable powder (WP) formulations
- 8.3.3 Solid water dispersible granules (WDG) formulations
- 8.3.4 Solid pellets, granules, microgranules (slow release) formulations
- 8.3.5 Solid substrates
- 8.4 Non-selective pre-enrichment
- 8.5 Selective enrichment [Go to Page]
- 8.5.1 After incubation of the initial suspension (primary enrichment in half-Fraser broth) for 25 h ± 1 h, 0,1 ml of the culture obtained in 8.4 shall be transferred to a tube or bottle containing 10 ml of secondary enrichment medium (Fraser broth) (described in B.3).
- 8.5.2 The inoculated medium (8.5.1) shall be incubated for 25 h ± 1 h at 37 °C ± 2 °C (6.3).
- 8.6 Plating out [Go to Page]
- 8.6.1 General [Go to Page]
- 8.6.1.1 From the primary enrichment culture (8.4) incubated for 25 h ± 1 h at 30 °C ± 2 °C (6.3), shall inoculate the surface of the first selective plating medium, Agar Listeria according to Ottaviani and Agosti (ALOA) (described in B.4), by means of a loop (6.5), to obtain well-separated colonies.
- 8.6.1.2 From the secondary enrichment medium incubated for 25 h ± 1 h at 37 °C ± 2 °C (6.3) (8.5.2), the procedure described in 8.6.1.1 shall be repeated with the two selective plating-out media.
- 8.6.1.3 The Petri dishes obtained in 8.6.1.1 and 8.6.1.2 shall be inverted and placed in an incubator set at 37 °C (6.3) for Agar Listeria according to Ottaviani and Agosti (B.4). For the second selective medium (B.5), follow the manufacturer’s instructions.
- 8.6.1.4 For Agar Listeria according to Ottaviani and Agosti (B.4), the plates shall be incubated for a total of 48 h ± 2 h at 37 °C ± 2 °C. If colonies of presumptive L. monocytogenes are evident at 25 h ± 1 h, the incubation may be stopped at this stage. For second selective agar the plates shall be incubated for the appropriate time. The dishes (8.6.1.3) shall be examined for the presence of presumptive colonies of L. monocytogenes.
- 8.6.2 Agar Listeria according to Ottaviani and Agosti (B.4)
- 8.6.3 Second selective medium
- 8.7 Confirmation of L. monocytogenes [Go to Page]
- 8.7.1 General
- 8.7.2 Selection of colonies for confirmation
- 8.7.3 Confirmation tests for L. monocytogenes [Go to Page]
- 8.7.3.1 The mandatory and optional tests to be performed for confirmation of presumptive L. monocytogenes are reported in Table 2
- 8.7.3.2 Catalase reaction (optional)
- 8.7.3.3 Motility test (optional)
- 8.7.3.4 Microscopic aspect (optional)
- 8.7.3.5 Haemolysis tests
- 8.7.3.6 CAMP test (optional)
- 8.7.3.7 Carbohydrate utilization
- 8.8 Interpretation of morphological and physiological properties and of the biochemical reactions
- 8.9 Additional characterization of isolated strains (optional)
- 9 Expression of results
- 10 Performance characteristics of the method [Go to Page]
- 10.1 Interlaboratory study
- 10.2 Sensitivity
- 10.3 Specificity
- 10.4 Positive predictive value (PPV)
- 10.5 Negative predictive value (NPV)
- 11 Test report
- 12 Quality assurance [Go to Page]
